Commercial vehicle tires having a belt that has two working plies and a cover ply are known to those skilled in the art. Normally, the belt of commercial vehicle tires has four plies, which include steel cords embedded in rubber compounds. In the case of a 4-ply belt, the radially innermost ply is referred to as the first belt ply or, according to its function, as a blocking ply. The second belt ply and the third belt ply are arranged radially on the outside of the first belt ply, acting as working plies. The radially outermost working ply is covered by the fourth belt ply, the cover ply.
In general, the steel cords of the first belt ply are at an angle of >45° to the circumferential direction. The first belt ply is referred to as a blocking ply because of its function of blocking the movement of the working plies in the circumferential direction. The steel cords of the two working plies are at an identical angle of between 15° and 30° to the circumferential direction of the tire, wherein the steel cords of one working ply slope in the opposite direction to the steel cords of the other working ply, relative to the circumferential direction of the tire. Thus, the steel cords of one working ply are arranged crosswise with respect to the steel cords of the other working ply. The working plies are subject to high shear forces and tensile forces and carry the principal load in the belt, and are therefore of particular importance for belt durability. The fourth belt ply has steel cords which enclose an angle of between 15° and 30° with the circumferential direction. The fourth belt ply, the cover ply, has the function of a protective ply for the two working plies situated thereunder since the cover ply forms a barrier to stones which can penetrate through the tread assembly. Without the cover ply, the cords of the working plies would be damaged by penetrating stones and would be subject to increased corrosion, something that would ultimately reduce the load capacity, durability and retread capacity of the tire.
The practice of providing steel cords of belt plies with a brass coating for better rubber adhesion is sufficiently well known. The steel cords of all the plies of multi-ply belts are always coated with the same brass composition. JP 60226303 A, for example, has disclosed the practice of providing the steel cords of all the belt plies of a radial tire with a brass coating which has a copper content of 60% by weight to 64% by weight. U.S. Pat. No. 4,732,197, for example, has disclosed the practice of providing the steel cords of all the belt plies of a radial tire with a brass coating which has a copper content of 60% by weight to 70% by weight.
It is furthermore known that a high copper content of the brass coating, while having a reduced adhesion, leads to improved corrosion resistance and that a low copper content of the brass coating, while having reduced corrosion resistance, leads to improved adhesion.